ZLD (zero liquid discharge) wastewater treatment

ABSTRACT

Methods and systems are provided for wastewater treatment that yields zero liquid discharge (ZLD). These include pre-treating provided wastewater from any contaminated water source to remove heavy metals, ultra-filtering the pre-treated wastewater to remove suspended and colloidal solids, nano-filtering the ultra-filtered wastewater to yield treated water (with monovalent ions) and a concentrate, treating the concentrate to remove di- and tri-valent elements and other compounds from the concentrate, and to reduce a level of sulfates to a specified level which is above a solubility level of sulfates—to yield returned water, and sludge, mixing the returned water with the provided wastewater before or at the first treatment stage and/or with the pre-treated wastewater before the ultrafiltration, and removing residual water from the sludge to yield removed solids with ZLD. Advantageously, disclosed processes and systems are efficient, cheaper and more sustainable than prior art systems.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.16/881,902, filed May 22, 2020.

BACKGROUND OF THE INVENTION 1. Technical Field

The present invention relates to the field of wastewater treatment, andmore particularly, to using nanofiltration and water recycling toachieve affordable and sustainable wastewater treatment.

2. Discussion of Related Art

Prior art industrial wastewater treatment systems typically applyreverse osmosis and special treatments to reach zero liquid discharge(ZLD, without any brine or concentrate being removed from the plant),see, e.g., FIGS. 6A and 6B below, however, such systems are often veryexpensive in construction and operation and are moreover often difficultto maintain.

For example, U.S. Patent Publication No. 20120205313, incorporatedherein by reference in its entirety, teaches sulfate removal from awater source by a reverse osmosis (RO) or nanofiltration (NF) processwhere the concentrate stream is treated with ferric chloride (FeCl₃) andcalcium chloride (CaCl₂) to precipitate and remove reject sulfate andrecycle the discharged concentrate water and any backwash water used toclean a filter used to prepare feed water for the RO or NF process andreach (non-ZLD) minimal liquid brine or concentrate release.

SUMMARY OF THE INVENTION

The following is a simplified summary providing an initial understandingof the invention. The summary does not necessarily identify key elementsnor limit the scope of the invention, but merely serves as anintroduction to the following description.

One aspect of the present invention provides a method of wastewatertreatment that yields zero liquid discharge (ZLD), the methodcomprising: pre-treating provided wastewater to remove heavy metals andsuspended and/or colloidal solids, providing pre-treated wastewater,ultra-filtering the pre-treated wastewater to remove suspended andcolloidal solids, nano-filtering the ultra-filtered wastewater to yieldtreated water and a concentrate, wherein the treated water comprisesmonovalent ions, treating the concentrate to remove di- and tri-valentelements and other compounds from the concentrate, and to reduce a levelof sulfates to a specified level which is above a solubility level ofsulfates—to yield returned water, and sludge, mixing the returned waterwith the provided wastewater before or at the first treatment stageand/or with the pre-treated wastewater before the ultrafiltration, andremoving residual water from the sludge to yield removed solids withZLD.

One aspect of the present invention provides a system for wastewatertreatment that yields zero liquid discharge (ZLD), the systemcomprising: a first treatment stage comprising: a first-stage treatmentunit configured to remove heavy metals and suspended and/or colloidalsolids from provided wastewater, and a filtration unit comprising: atleast one ultra-filtration unit configured to remove suspended andcolloidal solids from the pre-treated wastewater, and at least onenano-filtration unit configured to nano-filter the ultra-filteredwastewater to yield treated water and a concentrate, wherein the treatedwater comprises monovalent ions; a second treatment stage comprising: asecond-stage treatment unit configured to remove di- and tri-valentelements and other compounds from the concentrate, and to reduce a levelof sulfates to a specified level which is above a solubility level ofsulfates—to yield returned water, and sludge, and a final unitconfigured to remove residual water from the sludge to yield removedsolids with ZLD; and pipework configured to mix the returned water withthe provided wastewater at the first treatment stage, before, at and/orafter the first-stage treatment unit.

These, additional, and/or other aspects and/or advantages of the presentinvention are set forth in the detailed description which follows;possibly inferable from the detailed description; and/or learnable bypractice of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of embodiments of the invention and to showhow the same may be carried into effect, reference will now be made,purely by way of example, to the accompanying drawings in which likenumerals designate corresponding elements or sections throughout.

In the accompanying drawings:

FIGS. 1A and 1B are high-level block diagrams of systems for wastewatertreatment that yields zero liquid discharge (ZLD), schematicallyillustrating the main units, their functions and the flows in systems100, according to some embodiments of the invention.

FIG. 2 is a high-level schematic block diagram of systems for ZLDwastewater treatment that include using byproducts from the second stagein the first stage, according to some embodiments of the invention.

FIG. 3 is a high-level schematic block diagram of systems for ZLDwastewater treatment that illustrates monitoring and controllingcontaminants and flows in systems, according to some embodiments of theinvention.

FIGS. 4A-4E provide high-level schematic examples of embodiments ofsystems, according to some embodiments of the invention.

FIGS. 5A and 5B are high-level schematic illustration of FBRs(fluidized-bed reactors), according to some embodiments of theinvention.

FIGS. 6A and 6B are high-level schematic illustration of prior art ZLDwater treatment systems.

FIG. 7 is a high-level flowchart illustrating methods of wastewatertreatment that yields zero liquid discharge (ZLD), according to someembodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, various aspects of the present inventionare described. For purposes of explanation, specific configurations anddetails are set forth in order to provide a thorough understanding ofthe present invention. However, it will also be apparent to one skilledin the art that the present invention may be practiced without thespecific details presented herein. Furthermore, well known features mayhave been omitted or simplified in order not to obscure the presentinvention. With specific reference to the drawings, it is stressed thatthe particulars shown are by way of example and for purposes ofillustrative discussion of the present invention only, and are presentedin the cause of providing what is believed to be the most useful andreadily understood description of the principles and conceptual aspectsof the invention. In this regard, no attempt is made to show structuraldetails of the invention in more detail than is necessary for afundamental understanding of the invention, the description taken withthe drawings making apparent to those skilled in the art how the severalforms of the invention may be embodied in practice.

Before at least one embodiment of the invention is explained in detail,it is to be understood that the invention is not limited in itsapplication to the details of construction and the arrangement of thecomponents set forth in the following description or illustrated in thedrawings. The invention is applicable to other embodiments that may bepracticed or carried out in various ways as well as to combinations ofthe disclosed embodiments. Also, it is to be understood that thephraseology and terminology employed herein are for the purpose ofdescription and should not be regarded as limiting.

Embodiments of the present invention provide efficient and economicalmethods and mechanisms for handling wastewater and thereby provideimprovements to the technological field of wastewater treatment. Thetreated wastewater may be of any contaminated water source, such asindustrial wastewater, acid mine drainage (AMD), acid rock drainage(ARD), contaminated underground water, contaminated river water and soforth. Methods and systems are provided for wastewater treatment thatyields zero liquid discharge (ZLD). These include pre-treating providedwastewater to remove heavy metals and suspended and/or colloidal solids,ultra-filtering the pre-treated wastewater to remove suspended andcolloidal solids, nano-filtering the ultra-filtered wastewater to yieldtreated water (that include monovalent ions) and a concentrate, treatingthe concentrate to remove di- and tri-valent elements and othercompounds from the concentrate, and to reduce a level of sulfates to aspecified level which is above a solubility level of sulfates—to yieldreturned water, and sludge, mixing the returned water with the providedwastewater before or at the first treatment stage and/or with thepre-treated wastewater before the ultrafiltration, and removing residualwater from the sludge to yield removed solids with ZLD (without anybrine or concentrate being removed from the plant). Advantageously,disclosed processes and systems are efficient, cheaper and moresustainable than prior art systems. Specifically, disclosed processesand systems are advantageous with respect to prior art ZLD systems basedon multi-stage reverse osmosis and special treatment of remainingresidues with respect to both constructions costs (CAPEX—capitalexpenditure) and maintenance costs (OPEX—operation expenditure) and moreover make ZLD wastewater treatment affordable and sustainable.

Various embodiments are configured to treat a wide range of types ofwastewater, which may have various concentrations of a large number ofcontaminants. The systems and methods disclosed below may be adjusted,as explain below, to handle wastewater with these ranges ofcontaminations, providing ZLD. For example, metals and/or heavy metalssuch as Ag (typical value 0.1 mg/l, range up to 100 mg/l), Al (typicalvalue 0.5 mg/l, range up to 1000 mg/l). As (typical value 0.8 mg/l,range up to 100 mg/), Cd. Co, Cr, Mo, Ni (typical values 0.5 mg/l,ranges up to 100 mg/l), Cu, Mn (typical values 0.5 mg/l, ranges up to500 mg/l), Fe (typical value 1 mg/l, range up to 500 mg/l). Pb, Sb. Se,Sn, Ti, V (typical values 0.5 mg/l, ranges up to 5 mg/l) and Zn, V(typical value 0.5 mg/l, range up to 1000 mg/l)—typical to wastewaterfrom metal and mining industries—may be removed from the wastewater asdisclosed below. Related alkaline earth metals Mg (typical value 50mg/l, range up to 1000 mg/l) and Ca (typical value 120 mg/l, range up to2000 mg/l), as well as Be and Ba (typical values 0.5 mg/l, ranges up to5 mg/l) may also be removed. Other elements and compounds inmetal-related and other industrial processes include silica (SiO₂typical value 0.5 mg/L, range up to 10 mg/l), sulfates (SO₄ typicalvalue 500 mg/l, typical range between 500-10,000 mg/l), phosphates (PO₄typical value 1 mg/l, typical range up to 5 mg/l), cyanides (CN typicalrange up to 10 mg/), as well as carbonates (CO₃ typical value 10 mg/l,typical range up to 100 mg/l) and bicarbonates (HCO₃ typical value 20mg/l, typical range up to 100 mg/l) and nitrates (NO₃ typical value 20mg/l, typical range up to 100 mg/l)—all of which may be removed in theZLD processes and systems disclosed below. Other relevant elements andcompounds include F (typical value 0.5 mg/l, typical range up to 5 mg/l,also typical in metal-related industries), Cl (typical value 250 mg/l,typical range between 20-250 mg/l), nitrogen dioxide (NO₂ typical value5 mg/l, typical range up to 50 mg/), P (typical value 0.5 mg/i range upto 5 mg/), monovalent Na (typical value 150 mg/l, range between 20-250mg/l) and K (typical value 15 mg/l, range up to 100 mg/l), and B(typical value 0.5 mg/l, typical range up to 5 mg/l). Othercharacteristics of wastewater, which can be treated in disclosed systemsand methods below, include conductivity (typical value 2500 μs/cm,typical range between 1,000-20.000 μs/cm), pH (typical value 7.5,typical range between 1.5-12), total dissolved solids (TDS, typicalvalues 1.000-1.500 mg/l, typical range between 650-15,000 mg/l), totalsuspended solids (TSS, typical value 25 mg/l, typical range between1-1.000 mg/), turbidity (NTU, Nephelometric Turbidity Units, typicalvalue 50 NTU, typical range between 1-300 NTU) as well as color(platinum-cobalt scale, typical value 30 typical range between 1-300).Disclosed systems and methods may be configured and/or adjusted tomanage these characteristic according to given specifications, asdisclosed below. Clearly, as these ranges and compositions are veryversatile, adjustments of the disclosed systems and methods are shownbelow only for a few, non-limiting examples, which provide theprinciples for adjusting the disclosed systems and methods to treat anycomposition of wastewater that is required to be handled, for example,industrial wastewater, acid mine drainage (AMD), acid rock drainage(ARD), contaminated underground water, contaminated river water and soforth.

FIGS. 1A and 1B are high-level block diagrams of systems 100 forwastewater treatment that yields zero liquid discharge (ZLD),schematically illustrating the main units, their functions and the flowsin systems 100, according to some embodiments of the invention.

Systems 100 comprise a first treatment stage 110 and a second treatmentstage 120. First treatment stage 110 comprises a first-stage treatmentunit 102 configured to remove metals and/or heavy metals and optionallysuspended and/or colloidal solids (reduce TDS and/or TSS, and possiblyother contaminants, according to the wastewater quality) from providedwastewater 80, and filtration unit(s) 105 configured to filter thepre-treated wastewater to yield treated water that may includemonovalent ions 107 (and possibly some bivalent and/or trivalent ions atlow concentrations), and a concentrate 109. Second treatment stage 120comprises a second-stage treatment unit 125 configured to treatconcentrate 109 to remove mainly divalent ions and other compounds andelements that were not removed by first-stage treatment unit 102 (asspecified) and particularly to reduce a level of sulfates to a specifiedlevel which is above a solubility level of sulfates (e.g., 1500-2000ppm)—to yield returned water 121, and sludge 128. Second treatment stage120 further comprises a dewatering unit 103 (e.g., comprising a filterpress or a dewatering unit) configured to remove residual water fromsludge 128 to yield removed solids 129 with ZLD. The residual water maybe mixed back into treated water at various stages (see below). Systems100 further comprise pipework configured to mix returned water 121 withprovided wastewater 80 at first treatment stage 110, before, at or afterfirst-stage treatment unit 102. It is noted that while sulfates are usedherein as an illustrative example, other compounds, e.g., other divalentand/or trivalent ions (e.g., Mg⁺⁺) may be removed according to similarprinciples.

Second-stage treatment unit 125 may be configured to use calcium and/orcompounds of calcium and/or sodium such as calcium chloride or sodiumhydroxide (e.g., if chloride or sodium levels in wastewater 80 are low,respectively) to reduce the level of sulfates to the specified level ofsulfates, which may be between 2,000-5,000 ppm, or between 2,500-4,000ppm, or between similar ranges, depending on regulated required sulfatelevel reduction and system configuration. In various embodiments,second-stage treatment unit 125 may be configured to reduce the level ofsulfates to any of about a level of sulfates in provided wastewater 80,to a somewhat higher level (e.g., 110%, 120%, possibly up to 150%, orany intermediate value, as long as the concentrations stabilize overmultiple reiterations) or to a lower level (e.g., about 80%, 60%, 40%,20% or any intermediate fraction thereof), depending on the initialconcentration of the respective contaminant and the throughputs of therespective portions of water (e.g., resulting from performanceparameters of filtration units 105). In certain embodiments,second-stage treatment unit 125 may be configured to reduce the level ofsulfates to about a half of a level of sulfates in provided wastewater80. The level of reduction of sulfates in second-stage treatment unit125 may be derived from the throughput of concentrate 109 with respectto the throughput of wastewater 80 (see schematic example in Table 1below). In various embodiments, second-stage treatment unit 125 may beconfigured to use e.g., lime, Ca, CaO, Ca(OH)₂, CaCO₃, CaMg(CO₃)₂,possibly NaOH, or comparable compounds to remove sulfates. Correspondingchemicals may be used to remove other divalent and/or trivalent ions insecond-stage treatment unit 125. It is noted that the concentration ofthe removed compounds in concentrate 109 (e.g., two to three folds withrespect to wastewater 80) by filtration unit(s) 105, particularly bynanofiltration unit(s) 105B (see below), enables efficient removal ofcontaminants without having to cross the solubility threshold.

For example, in certain embodiments, first-stage treatment unit 102 mayconfigured to remove any of Cd. Al, Fe, Mn, Zn, As, Pb, Cu etc.,possibly adjust pH, remove some SO₄ and possibly any of Ca, Mg, CO₃,SiO₂ and so forth, and corresponding compounds thereof, depending onwastewater composition, contaminants' concentrations and the system'sspecific design. In certain embodiments, second-stage treatment unit 125may be configured to remove any of, e.g., SO₄, SiO₂, Ca, Mg, CO₃, andcorresponding compounds thereof, as well as suspended and colloidalsolids, and further adjust water parameters, depending on wastewatercomposition, contaminants' concentrations and the system's specificdesign.

While pipework is not illustrated explicitly, corresponding pipes,conduits, pumps, spigots, flow controllers, containers etc. are used toregulate the disclosed flows. Specifically flow 111 relates to the flowof feed wastewater 80 plus returned water 121 and flow 112 relates tothe flow of first-stage pre-treated water that is provided to filtrationunit(s) 105. Corresponding pipework and flow elements may be applied toregulate the disclosed flows. It is noted that the terms first treatmentstage 110 and second treatment stage 120 are used herein to indicate theunits and pipework used in the respective part of the treatmentfacility, and are therefore sub-systems within system 100. The term“unit” relating to the respective units in each of the stages, is usedherein to denote corresponding apparatuses that are used to treat water.e.g., receive water through pipework, modify the water content (e.g.,remove solids or particles, precipitate certain chemicals in the water,filter the water, etc., as referred to by respective unit descriptor),and deliver the treated water through pipework to another unit.

Referring to FIG. 1B, systems 100 may be configured to remove at leastheavy metals (possibly also any of SO₄, CO₃, HCO₃, Mg, Ca and othercontaminants) by first-stage treatment unit(s) 102, remove concentrate109 from pre-treated wastewater 112 by filtration unit(s) 105 which areconfigured to let monovalent ions (e.g., Na⁺, Cl⁻), and possibly somebivalent and/or trivalent ions at low concentrations, pass therethroughwith treated water 107, reduce sulfate levels (possibly also the levelsof any of Mg, Ca, and any other di-/tri-valent ions and othercontaminants) and remove other contaminants by second-stage treatmentunit 125, and return remaining dissolved sulfates in returned water tofirst stage 110. e.g., to be mixed with wastewater 80 to form flow 111,or possibly at least partly to be mixed with pre-treated water 112. Thesulfate levels (and levels of equivalent elements and compounds, e.g.,divalent ions) are reduce to a level above their solubility thresholdthat is low enough so that sulfates do not accumulate in the first stageand do not damage the membranes of filtration unit(s) 105, as disclosedbelow. In case divalent ions are left in treated water 107, their amountis a few percent at most of their amount in wastewater 80, e.g., 1-3% ofthe sulfates in wastewater 80 may remain in treated water 107, as longas their level is below the respective regulated requirements.Accordingly, at least 97-99% of the amount of sulfates in wastewater 80may be removed in solids 129. Correspondingly, concerning monovalentions, system 100 may be configured to pass 5-30% of their amount inwastewater 80 into treated water 107, avoiding accumulation ofmonovalent ions throughout the cycling and operation of system 100.

Table 1 provides a schematic example that illustrates treating a fewcontaminants by system 100, referring to stages of the processesillustrated in FIGS. 1A and 1B. The example is non-limiting as it refersto only a few contaminants (for simplicity), is schematic with respectto the flows and provides ranges for the contaminants after each stage.It is further noted that concentrations are typically building up andthen stabilizing through the system, as the mixing of the returned waterreadjusts the flows and concentrations. Table 1 provides ranges for anestimated stable state, following the initialization phase of system100. It is assumed that the feed flow to the plant is 100 m³/h, that thetotal plant recovery is between 95-97%, that nanofiltration (NF)recovery is between 55-65%, that Na and Cl ions permeate through to thetreated water and their concentration is similar to their concentrationin the feed water, and the concentration ranges are provided from asimulation after running it for over 10,000 cycles. The full ZLD processremoves heavy metals (Al, Fe, Mn, Cu, Zn, As, Cd, Mn, Cr, etc.) as foundin wastewater 80, as well as sulfates, magnesium, cyanides, calcium,etc.

TABLE 1 A schematic high-level illustrative example for treatingindustrial wastewater by the disclosed systems and processes. Stage ofprocess: Removal Following of heavy first-stage metals in treatment thefirst Returned and Treated Wastewater stage Concentrate water mixingwater (80) (112) (109) (121) (112) (107) Throughput 100 100* 54-82 54-82100* 95-97 (m³/h) Ion/ Ca⁺⁺ 550 See 1,200-1,500 500-700 550-600 10-30Element Na⁺ 85 following 1,000-1,500 1,000- 500-550 85 (mg/l) mixing*1,500 Mg⁺⁺ 500 1,000-3,500 300-500 400-500 10-20 SO₄ ⁻⁻ 3,500 8,000-12,000 3,500- 3,500- 100-200 4,500 4,000 Cl⁻ 31 400-500 400-500150-200 31 Al 0.5-5   <0.05 <0.05 <0.05 <0.05 <0.05 Fe  1-10 <0.05 <0.05<0.05 <0.05 <0.05 Mn 0.5-5   <0.05 <0.05 <0.05 <0.05 <0.05 Cu  10-100<0.05 <0.05 <0.05 <0.05 <0.05 *Concentrations following the mixing werecalculated according to the relative throughputs, assuming recoveryrates of 55-70% water 107 and 45-30% rejected concentrate 109.

It is noted that, following removal of heavy metals and possiblyadditional elements in first stage treatment 102, most mass of divalentions and other compounds is removed in second-stage treatment unit 125from concentrate 109. However, these are removed to a level above theirsolubility level (see, e.g., sulfates), using simple and fasttechnology, and the remaining contaminants are returned back to thereceived flow of wastewater 80 (or optionally after first-stagetreatment 102—to flow 112—as returned water 121 lack heavy metals). Asthe concentration of the remaining contaminants is about theirconcentration in provided wastewater 80, they do not accumulate, andtheir concentration does not rise about the level that is permitted byfiltration unit(s) 105. Filtrations unit(s) 105 remove thesecontaminants into concentrate 109, resulting in treated water withcontaminants level (e.g., sulfates) below the solubility level—withouthaving to apply the expensive prior art special treatment technologies95 to reduce their levels (see below). It is noted that theconcentrations of various elements and compounds throughout system 100depend on the system configuration, such as throughputs and number ofcycles through which the system is operated (in operation and insimulation) until steady state is reached.

In various embodiments, first-stage treatment unit 102 may be configuredto provide minor pre-treatment, e.g., only adjust the pH of the waterand remove heavy metals, or to provide more significant pre-treatment,e.g., also remove some of the sulfates and/or reduce any of TDS, TSS,turbidity, etc. In various embodiments, first-stage treatment unit 102may be configured to provide a level of pre-treatment that depends onthe quality of received wastewater 80 with respect to specifiedoperation requirements of filtration unit(s) 105. For example, if thelevel of sulfates in wastewater 80 is around 3000 ppm, no furtherreduction may be required at first stage 110, but if the level ofsulfates in wastewater 80 is around 10,000 ppm, first-stage treatment102 may be configured to reduce it to 3000-4000 ppm. It is noted that inany case, second-stage treatment unit 125 may be configured to removethe bulk of sulfates and/or equivalent contaminants (from concentrate109) to reach a level of sulfates that can be returned (121) to thereceived water (forming flow 111) without building up the sulfateconcentration at the first stage 110.

FIG. 2 is a high-level schematic block diagram of systems 100 for ZLDwastewater treatment that include using byproducts 127 from second stage120 in first stage 110, according to some embodiments of the invention.

In certain embodiments, filtration units 105 may compriseultrafiltration unit(s) 105A followed by nanofiltration unit(s) 105B,which are configured to remove concentrate 109 from the water whileletting monovalent ions (and possibly some bivalent and/or trivalentions at low concentrations) pass through with treated water 107. Forexample, filtration units 105 may comprise one or more ultrafiltration(UF) unit(s) 105A to remove or reduce the level of solids and colloidsin water 112 and one or more nanofiltration (NF) unit(s) 105B toselectively remove or reduce the level of bivalent ions and othercompounds in water 113. Backwash 106 from UF unit(s) 105A may bere-introduced into first stage treatment unit(s) 102 while concentrate109 from NF unit(s) 105B may be treated in second stage treatmentunit(s) 125.

It is noted that UF membranes typically remove colloidal and suspendedsolids in the water passing through it, while NF membranes typicallyreject most, or almost all of the divalent ions in the water passingthrough it, while passing through some of the monovalent ions (unlike ROmembranes that reject most or all of the monovalent ions). It is notedthat NF membranes used herein are such that pass through at least par ofthe monovalent ions, such as DuPont™ FilmTec™ NF90 or NF270 membranes.UF membranes typically have pore sizes greater than 10 nm (e.g., 10-50nm), may be made from polymeric (e.g., PVDF—polyvinylidene difluoride)hollow fibers for high mechanical strength and chemical resistance, andremove a wide range of particulates. NF is intermediate between UF andRO, may be made from thin-film composites (e.g., polyamide), typicallyremoving solutes down to a scale of 1 nm and rejecting organic moleculeswith molecular weights greater than 200-400, such as dissolved organics,endotoxins/pyrogens, insecticides/pesticides, herbicides, antibiotics,nitrates, sugars, latex emulsions, metal ions, etc., as well as solublesalts, e.g., at rates of 20-80% for monovalent anions (e.g., sodiumchloride or calcium chloride) and 90-98% for divalent anions (e.g.,magnesium sulfate). Thus, a nanofiltration unit has smaller pore sizesthan an ultrafiltration unit, for example less than 10 nm. It is furthernoted that the system configuration includes the degree to which wateris cycled through the respective membranes, influencing the resultingion concentration in the treated water. The more passes a certain amountof water carries out through a set on membranes, and/or the moremembranes are used for a given throughput, the lower is the resultingion concentration in the treated water.

Accordingly, treated water 107 may include additional elements orcompounds at low level, in particular sulfates below the solubilitythreshold (e.g., <1500-200 ppm, typically few hundred ppm at most,typically between 250-500 ppm, depending on regulatory requirements). Itis noted that prior art RO treatment results in water that is very pure,and usually requires post-process additions of minerals for varioususes, making permissible the residual low levels of elements andcompounds achieved by disclosed embodiments. In various embodiments. NFunit(s) 105B may let most monovalent pass through to treated water 107,while letting up to 1%, up to 3%, or possibly up to 5% or between 1-10%of one or more divalent or trivalent ions pass through.

It is noted that as concentrate 109 rejected from NF unit(s) 105B (andpossibly backwash water 106 from UF unit(s) 105A) is devoid of heavymetals, at least some of the water may be returned into first treatmentstage 110 after first-stage treatment 102.

In certain embodiments, sludge and/or solids 104, and/or any treatmentproducts 127 from second treatment stage 120 may be used inpre-treatment 102 of first treatment stage 110, e.g., to enhancecoagulation and/or flocculation in first stage treatment unit 102. Forexample, particles from particle-based second-stage treatment unit 125may be delivered as treatment products 127 to first-stage treatment unit102.

For example, second treatment stage 120 may comprise a fluid bedreactor. FBR 125C (see FIGS. 5A and 5B below), having solid granularmaterial that is fluidized by a fluid passed therethrough at highvelocities, and system 100 may be further configured to utilize used FBRsubstrate (e.g., coated particles 148 as treatment byproducts 127) infirst-stage treatment unit 102, for pre-treating provided wastewater 80.

FIG. 3 is a high-level schematic block diagram of systems 100 for ZLDwastewater treatment that illustrates monitoring and controllingcontaminants and flows in systems 100, according to some embodiments ofthe invention.

Systems 100 may further comprise monitoring units(s) 135 and one or morecontroller 130 that are configured to monitor flows throughout systems100 and possibly the levels of contaminants in the flows; and to controlthese flows and consequently the levels of contaminants in the flows,respectively—to maintain continuous operation of systems 100. Monitoringunit(s) 135 are illustrated schematically in a non-limiting manner withrespect to multiple flows 80, 111, 112, 107, 109, 128 and 121 in system100; clearly any internal flows (e.g., within filtration unit 105 suchas between UF unit(s) 105A and NF unit(s) 105B, see FIG. 2) andadditional flows may also be monitored with respect to their throughputand/or chemical composition. In certain embodiments, treatment byproducts 127 such as sludge 104 and/or coated particles 148 may also bemonitored. Monitoring unit(s) 135 may be interconnected among themselvesand to controller(s) 130 via various communication arrangements, e.g.,wire and/or wireless communication, via a communication link or network,via cloud services etc. Monitoring unit(s) 135 may be configured tomonitor the level of ions or other compounds in the various monitoredflows, and the data may be used by controller 130 to adjust the processaccording to requirements.

Controller(s) 130 may be configured to modify flows in system 100, andpossibly modify operational parameters of units in system 100 tomaintain the concentrations of contaminants within specified limits thatallow continuous operation of system 100 and maintain the membranes infiltration unit(s) 105 in good operational condition, reducingmaintenance costs. Controller(s) 130 may be further configured tomonitor a level of monovalent ions in treated water 107. In certainembodiments, controller(s) 130 may be configured to determine flows andcycling through system 100 to comply with regulatory requirementsconcerning levels of monovalent and/or divalent ions in treated water107, increasing the number of cycles for a given throughput to reducethe levels of monovalent and/or divalent ions in treated water 107.

In certain embodiments, controller(s) 130 may be operated with respectto predetermined simulation data that relate contaminant levels tothroughputs, making the control of contaminant levels simpler andallowing controller(s) 130 to mainly modify the flows through system100. It is noted that the concentrations of various elements andcompounds throughout system 100 depend on the system configuration, suchas throughputs and number of cycles through which the system is operated(in operation and in simulation) until steady state is reached.Controller 130 may be configured to regulate these throughputs andcycling in real-time and adjust operation parameters to reach requiredspecifications (e.g., thresholds for elements and compounds) in relationto parameters of received wastewater and system components.

FIGS. 4A-4E provide high-level schematic non-limiting examples ofembodiments of systems 100, according to some embodiments of theinvention. Elements from FIGS. 1A. 1B, 2, 3 and 4A-4E may be combined inany operable combination, and the illustration of certain elements incertain figures and not in others merely serves an explanatory purposeand is non-limiting.

FIG. 4A illustrates schematically certain embodiments of systems 100,comprising in first treatment stage 110, any of the following. Acoagulation mixer unit 102A and/or a flocculation unit 102B may be setbefore a precipitation unit 102C in first-stage treatment unit 102—toimprove pretreatment, e.g., by enhanced removal of heavy metals and/orsilicates and/or other contaminants, and optionally to remove dissolvedand/or colloidal solids. Water from precipitation unit 102C and/or waterremoved by a filtration and/or dewatering unit 103 from removedprecipitate 108 may be re-introduced into wastewater 80.

In various embodiments, sludge and/or solid material 104 fromprecipitation unit 102C and/or sludge/solid material 104 fromprecipitation unit 125C may be recycled and used, e.g., to enhanceflocculation and precipitation (using solid material 104 to yield highdensity sludge HDS). Sludge/solid material 104 from any one of first andsecond treatment stages 110, 120, respectively, may be used in the sameor in the other one of first and second treatment stages 110, 120,respectively, depending on the sludge composition and the treatmentrequirements.

At least one ultra-filtration (UF) unit 105A may be used. e.g., toremove dissolved and/or colloidal solids prior to at least onenano-filtration (NF) unit 105B in filtration unit(s) 105. UF unit(s)105A may be configured to provide initial filtrate 106 that may bedelivered back and added to wastewater 80 and/or to locations alongfirst-stage treatment unit 102 (e.g., flocculation unit 102B).

Certain embodiments of systems 100 may comprise in second treatmentstage 120, any of the following. A coagulation mixer unit 125A and/or aflocculation unit 125B may be set before a precipitation unit 125C insecond-stage treatment unit 125—to improve pretreatment, e.g., to removesulfates (above their solubility threshold). e.g., using calcium (e.g.,Ca. CaO, Ca(OH)₂, etc.) to yield gypsum, and to remove additionalcompounds such as divalent ions and/or silicates or other contaminants(see the list of common contaminants above). Treated water 107A may befully or partly added, as returned water 121, to treated wastewater 80before, at or after first-stage treatment unit 102 (first and thirdoptions illustrated in a non-limited manner). The exact details ofmixing depend on the quality of wastewater 80, of pre-treated wastewater112 and of treated water 107A—which may be controlled and adjusted(e.g., with respect to relative throughput) during the process.Returning water 121 reduces the level of sulfates and other contaminantsin pre-treated wastewater to enable the reduction of the level ofsulfates and enable continuous operation and low maintenance of themembranes in filtration unit(s) 105 (e.g., prevents clogging and otherdamage to the membranes).

Water from precipitation unit 125C and/or water removed by a filtrationand/or dewatering unit 103 (e.g., a filter press or a dewatering unit,similar to or different from the units used in first stage 110) fromsludge 128 may be re-introduced into concentrate 109 in second stage120, or into returned water 121, depending on its achieved quality.

FIG. 4B illustrates schematically that either or both first-stagetreatment unit 102 and/or second-stage treatment unit 125 may compriseany of coagulation and/or precipitation and/or flocculation units 118A.118B, 118C respectively, depending on the types and levels ofcontaminants that should be removed, on respective flow throughputs andon specified treatment requirements. Lime and/or limestone may be addedto any of the units, e.g., adjust the pH and remove sulfates in eitheror both first-stage treatment unit 102 and second-stage treatment unit125.

As illustrated schematically in FIG. 4B, in various embodiments,fluidized bed reactor(s) (FBRs) 140 may be used in either or both firstand second treatment stage(s) 110, 120 to remove one or morecontaminants from the respective treated water. FBRs 140 may be used inaddition to coagulation and/or flocculation and/or precipitation units118A. 118B, 118C respectively, or replacing any or all combinations ofthese, in either or both first-stage treatment unit 102 and/orsecond-stage treatment unit 125.

For example, FBRs 140 may be used in second-stage treatment unit 125 toyield fast removal of sulfates, using circulation through the fluidizedbed rather than precipitation, which is a much faster way to removecontaminants (e.g., 10-50 times faster). In certain embodiments, FBR(s)140 may be used to remove sulfates by using Ca or Ca compounds. e.g.,CaO, Ca(OH)₂, to reach sulfates levels lower than their solubilitylevel. Byproducts 127 from FBR 140 (e.g., costed particles 148, seebelow) may be used in first and/or second stage 110, 120, respectively,e.g., in flocculation and/or precipitation sub-units of first-stagetreatment unit 102 and/or second-stage treatment unit 125, as discussedabove. For example, coated particles 148 (see FIGS. 5A and 5B below)from FBR 140 may be used in units 102 and/or 125 to remove solids,elements and/or compounds as disclosed above, to recycle material andreduce the overall solids used in systems 100. For example, coatedparticles 148 from FBR 140 may be used in first-stage treatment unit 102to remove heavy metals.

In certain embodiments, FBRs 140 and HDS (High Density Sludge) treatmentunits 118D (which may also be implemented as precipitation units 118C)may be used in either or both treatment stages 102, 125 sequentially,with either FBRs 140 or HDS unit 118D used to treat the respective flowfirst, followed by the other type of treatment unit, e.g., to implementcoarse and then finer water treatment. Substrate from either FBRs 140 orHDS unit 118D may be used in any of treatment units 118A. 118B, 118C ofeither or both treatment stages 102, 125.

FIG. 4C illustrates schematically non-limited implementations offirst-stage treatment unit 102 and second-stage treatment unit 125, asfew options of the range illustrated schematically in FIG. 4B. Forexample, coagulation units 102D. 125D in units 102, 125, respectively,may correspond to coagulation units 118B in FIG. 4B. Returned water 121may be introduce to any of multiple locations throughout system 100,e.g., into coagulation unit 102A, flocculation unit 102B, pre-treatedwastewater 112 etc., and/or the throughputs to the respective optionallocations may be regulated by controller 130 according to monitoredparameters of the flows—to stabilize the process and enhance itsefficiency. Backwash water 106 from ultrafiltration unit(s) 105A may beintroduced back into wastewater 80 and/or be mixed within and/or afterfirst-stage treatment 102, as it is devoid of heavy metals—to furtherdilute sulfates and corresponding contaminants. Rejected concentrate 126from second-stage treatment unit 125 may be dewatered 103 directly(e.g., if concentrate is essentially sludge 128), and/or water therefrommay possibly be introduce into coagulation unit 125A in second stage 120and/or into coagulation unit 102A in first stage 110, depending onrequired regulation of flows and contaminants through system 100. It isnoted that for simplicity, the illustration in FIG. 4C merely showsoptional mixing points of returned water 121 and rejected concentrate126, assuming that the required pipework is added accordingly.

FIG. 4D illustrates schematically non-limiting implementations offirst-stage treatment unit 102 and of second-stage treatment unit 125with FBRs 140, according to some embodiments of the invention. FBR 140may be used in first-stage treatment unit 102 and/or in second-stagetreatment unit 125 alone, or possibly in addition to coagulation and/orflocculation units, as illustrated, e.g., in FIG. 4B. In any of theseembodiments, returned water 121 may be added to any of the incomingfluxes, such as flow 111 and/or concentrate 109, respectively,respective sludges 108, 128 may be dewatered to achieve ZLD and used FBRsubstrate 127 (e.g., coated particles 148 as treatment byproducts 127,see FIG. 5B) may be utilized in first-stage treatment unit 102 and/or insecond-stage treatment unit 125, e.g., in coagulation (mixer) unit 102Aand/or in coagulation (mixer) unit 125A, respectively. It is emphasizedthat multiple embodiments are included in FIG. 4D, as alternative flowsand components described therein may be used in various combinations.

FIG. 4E illustrates schematically reusing treated water 107 by afacility 81 from which wastewater 80 is received, according to someembodiments of the invention. In any of the disclosed embodiments, atleast a par of treated water 107 may be reused by facility 81 from whichwastewater 80 is received, to reduce water requirements of facility 81from the environment. It is emphasized that system 100 is properlybalanced to prevent excessive accumulation of monovalent ions, withoutrequiring an additional expensive treatment unit to remove monovalentions. Advantageously, reusing treated water reduces the environmentalfootprint of facility 81 and conserves natural water resources.

FIGS. 5A and 5B are high-level schematic illustration of FBR 140,according to some embodiments of the invention. FIG. 5A is a schematicperspective view in longitudinal cross section and FIG. 5B is aschematic longitudinal cross section with schematic examples forparticles before and after coating by contaminants 142, 148,respectively. FIGS. 5A and 5B merely illustrate one non-limiting examplefor FBR structure, equivalent structures may be used as well. FBRs 140utilize fine solid granular material 142 that is suspended in fastflowing treated water 109 and introduced chemicals 145 (e.g., lime, anyof CaO, Ca(OH)₂. CaCO₃, optionally NaOH)—to remove contaminants from thetreated water to yield treated water 121. It is noted that while priorart FBRs are used mainly to handle water hardness, disclosed FBRs 140may be used to remove sulfate and/or other divalent and/or trivalentions in a rapid process, that may simplify significantly ZLD watertreatment, while keeping the levels of these compounds low and withinrequirements by disclosed systems and processes.

For example, fine silicate sand 142 may be used to remove sulfates andother contaminants from concentrate 109, as part of second-stagetreatment unit 125. In certain embodiments, fine solid granular material142 such as silicate (SiO₂) or fine sand (e.g., in non-limitingembodiments, silica sand with grain diameter of 0.3-0.6 mm or naturalquartz No. 00, may be coated by sulfates and other contaminants duringthe treatment process in FBR 140 and be removed (148) from FBR 140following the process. Coated granular material 148 may then be used assubstrate in first-stage treatment unit 102 and/or in second-stagetreatment unit 125. Advantageously, coated granular material 148 maycomprise hydroxides (OH⁻) which may be used beneficially in first stagetreatment 102 to remove heavy metals. In various embodiments, FBR 140may be used in first-stage treatment unit 102 and/or in second-stagetreatment unit 125.

It is noted that FBRs 140 may be configured differently from prior artFBRs by introducing chemicals 145 through a conduit 146 that enters FBR140 from its top or central section and descends to the bottom of FBR140 to release chemicals 145 there. It is noted that in typical FBRs,chemicals 145 are introduced through a conduit that enters the FBR fromits bottom and ascends to release chemicals at the bottom sectionthereof. The disclosed change in design was found by the inventors to bemore efficient in disclosed FBRs 140 as it reduces clogging of thebottom of FBR 140 by coated particles 148 (typically some barrier ispresent at the bottom section of FBR 140 to prevent interruption to theintroduction of concentrate 109) and improved the flow through FBR 140.

Advantageously, FBRs 140 yield quick removal of large amounts ofsulfates and other contaminants from concentrate 109, e.g., when used insecond-stage treatment unit 125. It is noted that FBRs do not reduce thelevel of sulfates below their solubility level in water, as theremaining sulfates stay on the water returned (121) to first stagetreatment 110. For example, FBRs in second-stage treatment unit 125 mayreduce sulfate levels in concentrate 109 from, e.g., around 10.000 mg/lto around 4000 mg/l. In various embodiments, FBRs 140 in second-stagetreatment unit 125 may reduce sulfate levels in concentrate 109 from,e.g., a level between 5,000-40,000 mg/l to a level between 2,000-4,000mg/l. With respect to prior art treatment of concentrate 89 (see FIG. 6Abelow), FBR 140 may remove sulfates much faster (e.g., 5-10 timesfaster, possibly in minutes or few tens of minutes versus prior artseveral hours for precipitation units) and at much higher throughputs(e.g., 3-30 times larger) at the cost of not removing sulfates belowtheir solubility level as in the prior art.

FIGS. 6A and 6B are high-level schematic illustration of prior art ZLDwater treatment systems 90.

Prior art system 90 comprise multiple stages 91-93, each including apretreatment unit 82 that removes sediments and heavy metals (as sludgeor solid waste 97A) from received wastewater 80 and/or concentrate 89from a previous stage, followed by ultrafiltration in a RO (reverseosmosis) unit 85 that provides treated water 87 and removes all saltsfrom the wastewater in a concentrate 89, which is treated in a followingstage. It is noted that in prior art systems 90, multiple stages 91-93are required to reduce the volume of the brine (concentrate 89) producedby each stage, to reach a small throughput that then has to be speciallytreated to reach solid residues only.

For example, for 100 m³ wastewater 80, typically 60 m³ are produced astreated water 87 at a first purification stage 91, leaving 40 m³ asconcentrate 89 of first stage 91. Repeated stages 92, 93 removeadditional treated water 87 (e.g., additional 20 m³ and 10 m³,respectively) leaving more and more concentrated concentrate 89 (e.g.,20 m³ and 10 m³, respectively).

For zero liquid discharge (ZLD), the remaining concentrate 89 (e.g., ofstage 93), as well as possibly sludge 97A, undergoes special treatment95 which is usually expensive in both equipment and energy used—andresults in more treated water 87 and solid waste 97. Examples for priorart special treatment 95 comprise evaporation, freeze-crystallization,or other techniques, as well as chemical treatment discussed below,e.g., using aluminate gels that yield ettringite.

However, prior art treatment of industrial wastewater which may includea large concentration of waste products (e.g., heavy metals and varioussalts) is especially difficult, requiring multiple treatment stages,causing damage by overloading the delicate RO membranes, quicklyrendering them ineffective, and requiring complex special treatments 95such distillation, freeze-crystallization or chemical treatment—to treatthe remaining concentrate for ZLD. It is noted that these prior artspecial treatment methods are typically very expensive, and sometimeincrease the volume of solid waste 97 by addition of chemicals in theprocess (e.g., such as used in ion exchange technologies).

A particular difficulty in treating wastewater is their high content ofsulfates. Prior art methods (e.g., U.S. Patent Publication No.20120205313) reduce the content of sulfates below their solubilitythreshold (of ca. 1,500-2,000 ppm)—to under ca. 200-500 ppm (dependingon specific regulation) to provide treated water 87. A specific problemis the high cost of chemicals (e.g., aluminum compounds) that are usedto bind sulfates below their solubility threshold. It is further notedthat in contrast to prior art methods such as described in U.S. PatentPublication No. 20120205313, disclosed methods and system providecontinuous treatment of wastewater, without need for intermittentremoval of concentrate.

Prior art systems 90 typically have high CAPEX (capital expenditure) andhigh OPEX (operation expenditure). For example, in systems 90 treating500-600 m³/h, typically 60-70% of the CAPEX costs are used for specialtreatment 95 while only 30-40% of the costs are used for the RO stages.In contrast, disclosed systems 100 are expected to be at a similar costto only the RO stage of prior art systems 90, e.g., about a third thecost of prior art systems 90. Additional savings include smallerelectricity use (estimated <1 Kw/m³ feed for disclosed systems 100versus prior art costs of 2-3 Kw/m³ feed for systems 90, mainly forspecial treatment 95 which typically require 15-50 Kw for 1 m³concentrate) and much lower cost for added chemicals. Moreover, priorart systems 90 use larger amount of chemicals to remove sulfates, e.g.,larger amounts of Ca and Al to form in the treatment system the compoundettringite—a hydrous calcium aluminum sulfate mineral with the formula:Ca₆Al₂(SO₄)₃(OH)₁₂.26H₂O—requiring CaO and Al(OH)₃ to remove SO₄ byconversion in a complex chemical process. It is noted that Al(OH)₃ istypically required in the prior art as amorphous gel that is anexpensive compound.

In contrast, in disclosed systems 100, all SO₄ is removed e.g., as CaSO₄or gypsum. The stoichiometric balance is 1 mol Ca for 1 mol of removedSO₄ versus prior art ratio requiring 2 mol Ca and 2/3 mol Al for each 1mol of removed SO₄. Therefore, removed solids 129 also have a muchsmaller mass than prior art solid waste 97 (possibly less than one halfthereof), providing an additional significant advantage.

Moreover, ettringite is commonly recycled in prior art systems 90 toregenerate the aluminum hydroxide gel, using acids in an additionalprocess—which further increase prior art CAPEX, OPEX and resultingchemical waste. In contrast, in certain embodiments, removed solids 129of disclosed systems 100 may comprise mainly gypsum (CaSO₄) at arelatively high purity (e.g., above 95%, depending on the contaminantsin wastewater 80). Gypsum sludge (128, e.g., with 30-50% water content,or 129, dried) may be produced at ca. 5 tons sludge per hour by a 500m³/h system 100, making a total of about 1% of processes wastewatervolume. Advantageously, gypsum sludge 128 may be used in variousindustries (e.g., for cement, construction or agriculture) as it is,without need for further processing, and be directly sold. Using FBRs140, resulting coated particles 148 (see FIG. 5B) may comprisegypsum-coated silica grains, that are effective in removing heavy metalsin first-stage treatment unit 102, either as is or after activation,e.g., with ferric material (e.g., ferric sulfates and/or chlorides)and/or due to high content of hydroxides.

Due to the high OPEX and required high maintenance for the RO membranes,in practice, prior art industrial wastewater treatment facilitiescommonly become non-operational within a relative short period of theirestablishment, especially in developing countries, due to high operationand maintenance costs.

Advantageously, disclosed embodiments overcome the prior artlimitations, to provide economical and efficient zero liquid dischargetreatment of wastewater. Disclosed embodiments manage and balance levelsof salts and especially of sulfates throughout the treatment process andfacility to reach sustainable and economical treatment of heavilypolluted wastewater.

Specific enablers for the advantages provided by disclosed systems 100include:

-   (i) In first treatment stage 110, RO membranes and modules are    replaced by ultrafiltration and/or nanofiltration membranes and    modules which allow monovalent ions through into treated water 107.    Disclosed systems 100 monitor and control the level of monovalent    ions in treated water 107 to verify they do not exceed regulated    levels. Reducing the level of purity of water 107 with respect to    prior art treated water 87 maintains the acceptability of water 107    and simplifies treatment of concentrate 109 as it dismisses with the    prior art need to precipitate the monovalent ions in later treatment    stages 92-94. Divalent ions (e.g., sulfates) are left in concentrate    109. Specifically, when treating hard wastewater, using    nanofiltration membranes is advantageous to using RO membranes with    respect to expected operative life of the membranes and maintenance    costs.-   (ii) Sulfates are removed from concentrate 109 in main treatment    125, which reduces sulfate concentration but not below the    solubility threshold as in the prior art. For example, second    treatment stage 120 may be configured to reduce the level of    sulfates to 2,000-4,000 ppm. Advantageously, much simpler methods of    sulfate removal may be used, e.g., precipitation using calcium    and/or is much cheaper than prior art methods of reducing the level    of sulfates below their solubility threshold (e.g., HDS—High Density    Sludge treatment methods). Returned water 121 may then be mixed in    first stage 110 with received wastewater 80, which typically have    similar or higher levels of sulfates (e.g., 4,000-10.000 ppm), so    that the reduced level of sulfates is viably maintained and does not    accumulate in system 100. An additional advantage resulting from the    simpler sulfates removal process is that disclosed systems 100 and    processes 200 are less limited, or not limited at all in size and    throughput of wastewater 80.-   (iii) Main treatment 125 may be modified with respect to prior art    treatment 82 by using FBR 140 that makes the precipitation process    much quicker (e.g., typically takes minutes instead of prior art    processes that take hours)—and sufficient for the relaxed    requirements concerning the sulfate level reduction. Sulfates    removal and FBR 140 may be used as alternatives or may be both used    for partial treatment 125.-   (iv) Some of the treatment byproducts 127 from stage 120 may be used    in first-stage treatment unit 102 of stage 110 to further enhance    pretreatment. For example, CaSO₄ and/or used (coated) solid granular    material 148 from FBR 140 may be used as coagulant in first-stage    treatment unit 102.

Further advantage is provided by controller 130 that may be configuredto monitor and regulate the flows throughout system 100, maintaininglevels of specified ions and compounds within specified ranges. e.g.,sulfates, monovalent ions, silica, metal ions, calcium. In particular,controller 130 is configured to provide treated water 107 withinspecifications, control the quality of returned water 121 that istransferred from stage 120 into pretreatment 102 in stage 110, controlthe optional transfer of treatment products 127 from stage 120 intopretreatment 102 in stage 110, and monitor efficiency and maintenance ofnanofiltration modules 105.

FIG. 7 is a high-level flowchart illustrating methods 200 of wastewatertreatment that yields zero liquid discharge (ZLD), according to someembodiments of the invention. The method stages may be carried out withrespect to systems 100 described above, which may optionally beconfigured to implement methods 200. Method 200 may comprise thefollowing stages, irrespective of their order.

Method 200 may comprise treating wastewater (of any contaminated watersource, such as industrial wastewater, acid mine drainage, contaminatedunderground water, contaminated river water etc.) to yield zero-liquiddischarge (ZLD) (stage 210) by pre-treating provided wastewater toremove heavy metals (and possibly other contaminants, according to thewastewater quality), remove suspended and/or colloidal solids (reduceTDS and/or TSS) and possibly remove divalent ions such as sulfates(stage 220), ultra-filtering the pre-treated wastewater to removesuspended and colloidal solids (stage 225), nano-filtering theultra-filtered wastewater to remove divalent ions (e.g., sulfates) andyield treated water (that may include monovalent ions and some divalentions) and a concentrate (stage 230), treating the concentrate to removedi- and tri-valent elements and other compounds from the concentrate,and to reduce a level of sulfates to a specified level which is above asolubility level of sulfates—to yield returned water, and sludge (stage240), mixing the returned water with the provided wastewater before orat the first treatment stage and/or with the pre-treated wastewaterbefore the ultrafiltration (stage 250) and removing residual water fromthe sludge to yield removed solids with ZLD (stage 255). In certainembodiments, method 200 may further comprise using removed sludge forthe pre-treatment of the provided wastewater and/or for treatment of theconcentrate (stage 254).

In certain embodiments, method 200 may further comprise controllinglevels of compounds in the treated water to continuously reiterate thestages of method 200 (stage 260).

In certain embodiments, method 200 may comprise treating the concentrateusing calcium and/or calcium and/or sodium compounds (e.g., any of Ca,CaO, Ca(OH)₂, CaCO₃, NaOH in particular cases in which Na level inwastewater 80 is low, CaCl₂) (or possibly other chlorides) in particularcases in which Cl level in wastewater 80 is low etc.) to reduce thelevel of sulfates (sage 246). For example, method 200 may comprisekeeping the specified level of sulfates between 2,000-5,000 ppm orbetween 2.500-4,000 ppm and/or at about a half of a level of sulfates inthe provided wastewater (sage 248), depending on regulated requiredsulfate level reduction and system configuration. In certainembodiments, method 200 may comprise treating the concentrate with afluid bed reactor (FBR) (stage 242) and optionally utilizing used FBRsubstrate for the pre-treatment of the provided wastewater (stage 244).The FBR may be used to provide the full treatment of the concentrate orto provide a partial treatment of the concentrate, accompanied by, e.g.,coagulation and/or flocculation treatment.

In certain embodiments, method 200 may comprise monitoring a level ofmonovalent ions in the treated water (stage 270), and reducing the levelthereof if needed (stage 272).

In certain embodiments, method 200 may further comprise delivering atleast part of the treated water for reuse in a facility providing thewastewater (stage 275).

It is noted that specific values may be modified and are understood toencompass ±10% of the respective values.

In the above description, an embodiment is an example or implementationof the invention. The various appearances of “one embodiment”, “anembodiment”, “certain embodiments” or “some embodiments” do notnecessarily all refer to the same embodiments. Although various featuresof the invention may be described in the context of a single embodiment,the features may also be provided separately or in any suitablecombination. Conversely, although the invention may be described hereinin the context of separate embodiments for clarity, the invention mayalso be implemented in a single embodiment. Certain embodiments of theinvention may include features from different embodiments disclosedabove, and certain embodiments may incorporate elements from otherembodiments disclosed above. The disclosure of elements of the inventionin the context of a specific embodiment is not to be taken as limitingtheir use in the specific embodiment alone. Furthermore, it is to beunderstood that the invention can be carried out or practiced in variousways and that the invention can be implemented in certain embodimentsother than the ones outlined in the description above.

The invention is not limited to those diagrams or to the correspondingdescriptions. For example, flow need not move through each illustratedbox or state, or in exactly the same order as illustrated and described.Meanings of technical and scientific terms used herein are to becommonly understood as by one of ordinary skill in the art to which theinvention belongs, unless otherwise defined. While the invention hasbeen described with respect to a limited number of embodiments, theseshould not be construed as limitations on the scope of the invention,but rather as exemplifications of some of the preferred embodiments.Other possible variations, modifications, and applications are alsowithin the scope of the invention. Accordingly, the scope of theinvention should not be limited by what has thus far been described, butby the appended claims and their legal equivalents.

What is claimed is:
 1. A method of wastewater treatment that yields zeroliquid discharge (ZLD), the method comprising: pre-treating providedwastewater to remove heavy metals and suspended and/or colloidal solidsto provide pre-treated wastewater, ultra-filtering the pre-treatedwastewater to remove suspended and colloidal solids, nano-filtering theultra-filtered wastewater to yield treated water and a concentrate,wherein the treated water comprises monovalent ions, treating theconcentrate to remove di- and tri-valent elements and other compoundsfrom the concentrate comprising adding sulfate removal compounds, thesulfate removal compounds consisting of CaO, Ca(OH)₂ and/or CaCO₃ toreduce a level of sulfates to a specified level which is above asolubility level of sulfates—to yield returned water having a level ofsulfates which is above a solubility level of sulfates, and sludge,mixing the returned water having a level of sulfates which is above asolubility level of sulfates with the provided wastewater before or atthe first treatment stage and/or with the pre-treated wastewater beforethe ultrafiltration, removing residual water from the sludge to yieldremoved solids with ZLD, wherein no concentrate or brine is discharged,and carrying out the method continuously while controlling levels ofcompounds in the treated water.
 2. The method of claim 1, furthercomprising treating the concentrate with a fluid bed reactor (FBR).
 3. Amethod of wastewater treatment that yields zero liquid discharge (ZLD),the method comprising: pre-treating provided wastewater to remove heavymetals and suspended and/or colloidal solids to provide pre-treatedwastewater, ultra-filtering the pre-treated wastewater to removesuspended and colloidal solids, nano-filtering the ultra-filteredwastewater to yield treated water and a concentrate, wherein the treatedwater comprises monovalent ions, treating the concentrate to remove di-and tri-valent elements and other compounds from the concentrate, and toreduce a level of sulfates to a specified level which is above asolubility level of sulfates—to yield returned water having a level ofsulfates that is above a solubility level of sulfates, and sludge,mixing the returned water having a level of sulfates that is above asolubility level of sulfates with the provided wastewater before or atthe first treatment stage and/or with the pre-treated wastewater beforethe ultrafiltration, and removing residual water from the sludge toyield removed solids with ZLD, wherein the treating of the concentratecomprises using calcium, calcium compounds and/or sodium compounds toreduce at least the level of sulfates, further comprising treating theconcentrate with a fluid bed reactor (FBR), and further comprisingutilizing used FBR substrate for the pre-treatment of the providedwastewater.
 4. The method of claim 1, wherein the specified level ofsulfates is between 2,000-5,000 ppm.
 5. The method of claim 1, whereinthe specified level of sulfates is about a half of a level of sulfatesin the provided wastewater.
 6. The method of claim 1, further comprisingmonitoring a level of monovalent ions in the treated water, and reducingthe level thereof if it exceeds a specified threshold.
 7. The method ofclaim 1, wherein the provided wastewater comprises at least one of:industrial wastewater, acid mine drainage (AMD), acid rock drainage(ARD), contaminated underground water, contaminated river water.
 8. Themethod of claim 1, further composing delivering at least part of thetreated water for reuse in a facility providing the wastewater.
 9. Asystem for wastewater treatment that yields zero liquid discharge (ZLD),the system comprising: a first treatment stage comprising: a first-stagetreatment unit configured to remove heavy metals and suspended and/orcolloidal solids from provided wastewater to provide pre-treatedwastewater, and a filtration unit comprising: at least oneultra-filtration unit configured to remove suspended and colloidalsolids from the pre-treated wastewater, and at least one nano-filtrationunit configured to nano-filter the ultra-filtered wastewater to yieldtreated water and a concentrate, wherein the treated water comprisesmonovalent ions; a second treatment stage comprising: a second-stagetreatment unit configured to remove di- and tri-valent elements andother compounds from the concentrate, the second-stage treatment unitcomprising added sulfate removal compounds, the added sulfate removalcompounds consisting of CaO, Ca(OH)₂ and/or CaCO₃ thereby reducing alevel of sulfates to a specified level which is above a solubility levelof sulfates—to yield returned water having a level of sulfates above thesolubility level of sulfates, and sludge, and a final unit configured toremove residual water from the sludge to yield removed solids with ZLD,wherein no concentrate or brine is discharged from the system, acontroller configured to control levels of compounds in the treatedwater to maintain continuous operation of the system, and pipeworkconfigured to mix the returned water having a level of sulfates abovethe solubility level of sulfates, at the first treatment stage, with theprovided wastewater and/or with the pre-treated wastewater.
 10. Thesystem of claim 9, wherein the second-stage treatment unit reduces thelevel of sulfates to the specified level of sulfates which is between2,000-5,000 ppm.
 11. The system of claim 9, wherein the second-stagetreatment unit is configured to reduce the level of sulfates to about ahalf of a level of sulfates in the provided wastewater.
 12. The systemof claim 9, wherein the second treatment stage comprises a fluid bedreactor (FBR), and wherein the system is further configured to utilizeused FBR substrate in the first-stage treatment unit, for pre-treatingthe provided wastewater.
 13. The system of claim 9, wherein thecontroller is further configured to monitor a level of monovalent ionsin the treated water, and the system is further configured to reduce thelevel thereof if it exceeds a specified threshold.
 14. The system ofclaim 9, wherein the provided wastewater comprises at least one of:industrial wastewater, acid mine drainage (AMD), acid rock drainage(ARD), contaminated underground water, contaminated river water.
 15. Thesystem of claim 9, wherein at least one of the first-stage treatmentunit and the second-stage treatment unit comprises both a fluid bedreactor (FBR) and a HDS (High Density Sludge) treatment unit configuredto sequentially treat a respective flow.